Brightness / Luminance / Illuminance

To describe light intensity there are a number of terms such as brightness, luminance and illuminance… These expressions describe different aspects of light intensity. This article concentrates on introductory information relevant to photography

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Analog as well as digital systems can only display a restricted range of brightness (brightness ratio from the brightest and darkest part of the subject and exceedance results a homogenous white area – non-exceedance results in a homogenous black area).  Light must be metered in photography and settings such as diaphragm, exposure and ISO rate must be set accordingly. For more information on this, see exposure and exposure metering. As well as the light source’s (luminance / illuminance) brightness, other aspects such as distance to subject, atmospheric composition (possible pollution…), the subject’s reflective properties and also the surrounding area are of importance (e.g. optical brighteners, other dark or light surface areas that absorb or reflect light).
In photography, reduced brightness creates difficulties. This becomes apparent when undesired motion blurring occurs and/or the images are underexposed and/or blurred. There is a range of possibilities that can used to conquer these problems. Creative suggestions on how to do that can be found here, on the Keywords are e.g., flash-drag effect, zoom effect, tripod, diaphragm, ISO rate… It is impossible to create a comprehensive list; nearly every technical aspect of photography has something to do with this topic.

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